FISHPAC 2010 USBL Testing Report - Alaska Fisheries Science

20 Pages·2010·0.96 MB·English

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Cruise Report for 2010 USBL Testing
Strait of Juan de Fuca, Washington
Prepared by: RACE Division Habitat Research Group
Cruise ID: FISHPAC Vessel(s): NOAA Ship Fairweather
Cruise Dates: June 28 – July 2, 2010 Project Number: OPR-N324

Alaska Fisheries Science Center
7600 Sand Point Way NE
Seattle, WA 98115-6349
2 November 2010
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Overview
The Magnuson-Stevens Fishery Conservation and Management Act requires the National Marine
Fisheries Service (NMFS) to characterize and map essential fish habitat and to protect these areas
from adverse impacts due to fishing and other activities. The Alaska Fisheries Science Center
(AFSC) conducts this research in the Bering Sea, Gulf of Alaska, and Aleutian Islands. NOAA’s
Office of Coast Survey (OCS) is responsible for providing navigation products and information for
transportation safety in these same areas. Since 2006, scientists with the AFSC’s FISHPAC project
have been working collaboratively with OCS and NOAA Ship Fairweather (FA) to integrate the
ocean mapping activities of these two organizations in the eastern Bering Sea (EBS). This work
involves a variety of towed instruments, including two different side scan sonar systems (Klein 5410,
Klein 7180 LRSSS), a towed camera system (TACOS), and an over-the-side grab sampler
(SEABOSS). In all cases, a subsurface tracking system is required to provide accurate positioning of
the overboard system and the resulting data.
Ultra-short baseline (USBL) systems calculate the subsurface position of an object by combining
acoustic range and bearing data from a vessel-mounted transceiver with attitude, heading and
location information from the vessel’s own navigation system. The object to be tracked needs to be
equipped with an acoustic transponder or responder that communicates with the transceiver
attached to the vessel. This technology does not require a transponder array to be deployed on the
seabed before positioning can commence and is thus ideal for trackline work.
The AFSC purchased a wideband-enabled Sonardyne Fusion USBL system for FA in 2004 in order
to provide capability for subsurface positioning of scientific and hydrographic instruments. In 2006,
an over-the-side pole was fabricated by a third party using a proven AFSC design, and was
successfully used during extended at-sea operations in the EBS. This same pole catastrophically
failed shortly after deployment in 2008. The USBL transceiver was subsequently installed in a
vacant area of the ship’s skeg during FA’s 2008-2009 winter-repair period. Performance problems
associated with acoustic interference and multipath conditions were identified during sea trials in
Puget Sound on 23 April 2009.
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Figure 1. Towed scientific and hydrographic instruments that require subsea
positioning capability (clockwise from upper let): Klein 5410 side scan sonar, Klein
7180 long-range side scan sonar, SEABOSS sediment grab/camera system, and the
two-part TACOS video sled.

Field operations in 2010 tested performance characteristics of the wideband-enabled Sonardyne
Fusion USBL system installed on FA. In particular, various subsea-positioning scenarios were
investigated for equipment that is required by the FISHPAC project and future hydrographic
surveys (Figure 1).
Objectives
(1) Investigate performance of the skeg-mounted USBL transceiver on FA for subsea
positioning of a Klein 5410 side scan sonar at various tow speeds and layback angles.
(2) Investigate performance of the skeg-mounted USBL transceiver on FA for subsea
positioning of a Klein 7180 LRSSS at various tow speeds and layback angles.
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(3) Investigate performance of the skeg-mounted USBL transceiver on FA for subsea
positioning of the TACOS video sled at minimum vessel speed.
Vessels and Gear
Operations were conducted aboard FA, a multi-mission hydrographic survey vessel capable of
continuous sonar operations.
The wideband-enabled Sonardyne Fusion USBL system on FA consists of three general
components: (1) programmable transponders for the towed instruments, (2) a digital transceiver
mounted with 0.2 m clearance from the hull and approximately 5 m forward of the ship’s propellers,
and (3) a rack-mounted topside system for data processing. Component details and operational
settings are presented in Table 1. In general, USBL replies were captured in Ranger software and
passed via serial cable to QINSy integrated-navigation software during acquisition. The resulting
position data were extracted from the QINSy databases during post-processing.
Table 1. Specifications for the Sonardyne USBL system components. Rx refers to the receive frequency that was used.
Component Model / Version Settings
Rx – 32 kHz (Klein 7180)
Transponder, wideband directional 8070 WSM
Rx – 33 kHz (Klein 5410)
Transponder, wideband omni-directional 8071 WSM Rx – 30.5 kHz
Digital transceiver, hemispherical 8021 ± 90 degree coverage
Navigation Control Unit 8020
COMPATT Mk4 transponder with
7800 MF Rx – 31.6 kHz
acoustic release and floatation collar
Calibration software CASIUS ver. 5.0.1.8
Acquisition and processing software Ranger ver. 2.02
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Two different side scan sonar systems and a towed video system were used to evaluate the
performance of FA’s USBL system. The Klein 5410 is a high-resolution interferometric side scan
sonar (455 kHz) and the Klein 7180 LRSSS (180 kHz) is a prototype long-range side scan sonar with
an integrated multibeam echosounder and an independent 38 kHz single-beam echosounder
incorporated into the towfish. Each towfish was deployed with its respective depressor wing. The
third instrument tested was the Towed Auto-Compensating Optical System (TACOS), a two-part
towed camera sled that is used to create high-quality downward-looking video mosaics to support
interpretation of site-specific seafloor information obtained with the sonars. Subsea positioning of
SEABOSS was not included in this exercise because of acceptable performance during the 2009
FISHPAC-project cruise in the EBS. 1

Itinerary
27 – 29 May Mobilize AFSC equipment at USCG pier 36, Seattle, Washington.
28 June Embark FA, Neah Bay, Washington.
29 -30 June USBL testing aboard FA, Strait of Juan de Fuca, Washington.
1 July Transit to Manchester fuel depot and USCG pier 36, Seattle,
Washington.
2 July Demobilize and transport all field gear to the AFSC.

1 Fairweather project M-R908, 26 July – 7 August 2009. The cruise report is available at
http://www.afsc.noaa.gov/RACE/surveys/cruise_archives/cruises2009/results_Fairweather_FISHPAC-2009-01.pdf
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n

Figure 2. USBL testing area in the Strait of Juan de Fuca.
Study Area
The 2010 study area was located in the Freshwater Bay region of the Strait of Juan de Fuca,
Washington (Figure 2). It lay within the eastbound ‘recommended two-way traffic’ area and was
approximately 1 nm south of the main traffic lanes. The seabed in the area was generally flat with
depths ranging from 120-150 m.
Methods
A testing program was undertaken to define the performance characteristics of the skeg-mounted
USBL transceiver on FA. For each of the three towed instruments, specific combinations of speed
over ground (SOG) and bearing from the vessel trackline were tested (Table 2). The range of SOG
values, in 2 kt increments for the sonars, covered the standard operating scenarios for acquiring
high-quality data with each system. Different layback angles were tested to produce variability in
position of the towfish relative to the vessel. This variability routinely occurs when cross currents
and winds displace the vessel from the fixed navigation line for the towed device. In practice,
layback distance was not a controlled factor and varied as a function of water depth, the amount of
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cable-out needed to obtain the desired altitude, the position of the depressor wing (fixed for these
tests) and the environmental conditions. Layback distance for the TACOS sled was minimal, in
keeping with normal practice. USBL testing was originally scheduled to occur during routine
hydrographic operations in the Olympic Coast National Marine Sanctuary (OCNMS). However,
early completion of that work enabled dedicated maneuvers in more protected waters near
Freshwater Bay.
Table 2. Test conditions for evaluating USBL performance. Layback angle refers to instrument position relative to the
heading of the vessel, that is, whether it is towing directly behind the vessel (None), is offset to port (OTP) or is offset
to starboard (OTS). The USBL system was operated in transponder mode.
Instrument Altitude Layback Angle SOG (kts) Transponder
Klein 7180 70-120 m 2 None, OTS, OTP 4 - 10 Directional
TACOS 1 m Random 1 Omni-directional
Omni-directional,
Klein 5410 30-80 m None, OTS, OTP 4 - 10
Directional

A reconnaissance survey was conducted with the ship’s Reson 7111 multibeam echosounder to
identify potential hazards in the study area. A dynamic calibration of the USBL system, preceded by
a single CTD cast, was completed to determine system offsets and provide accurate positioning
capability. Although FA’s navigation reference frame was precisely determined during a March 2009
centerline survey by NGS, the USBL reference point remains estimated since the transceiver was
installed after the NGS survey was completed. The USBL calibration involved anchoring a
COMPATT transponder with a floatation collar and acoustic release in the center of the study area.

2 Optimum altitude-layback conditions have not been determined for this system. The manufacturer recommends an
altitude of 120 m for maximum range, 70-80 m altitude for 100 m water depth (i.e. towfish depth is 20-30 m so as to
isolate it from surface effects), and the overall maximum altitude is 200 m.
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Towfish “off to Towfish “off to
starboard” (OTS) port” (OTP)

Figure 4. Schematic of the X-shaped maneuvering pattern

used to measure USBL system performance while towing
a side scan sonar. Straightaway legs of the X were
Figure 3. Example of transit lines used to collect USBL approximately 700 m in length.
calibration data.

This served as the calibration point for a box-in procedure to quantify total system errors between
the ship and USBL reference frames. Once deployed, the vessel was navigated in a pattern similar to
Figure 3, passing over each of the cardinal points while maintaining a good heading. Twelve
calibration lines were run in all – eight transits between adjacent cardinal points in both directions
(i.e. north-west, west-south, south-east, east-north, north-east, east-south, south-west, and west-
north), and two tracklines each crossing over the beacon in both directions. Sonardyne’s CASIUS
software (Table 1) was then used to determine the calibration corrections for the transceiver
installation. Once a satisfactory solution was obtained, the acoustic release was activated and the
COMPATT unit floated to the surface for recovery.
USBL performance while towing the side scan sonar systems was measured on a fixed X-shaped
maneuvering pattern (Figure 2, Figure 4) where the test conditions for each pass varied according to
the predetermined plan for each instrument (Table 2). A complete circuit of the X and the two
accompanying turns was completed at each test speed. The maneuvering pattern was continuously
navigated with a particular towfish until testing with that system was completed. The first run of
each set began with the vessel drifting and the towfish hanging at the prescribed altitude. Vessel
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speed was then slowly increased to 4 kts enabling system-performance measurements as a function
of towfish angle from the water surface. Vessel speed was raised to the next test speed when lined-
up for the next circuit around the pattern. The arms of the X were defined by fixed points with
unspecified turning arcs at each end. This provided positioning information with the towfish
tracking astern and when offset to port and starboard (as frequently happens when navigating a
towfish rather than the vessel along a trackline). Cable-out was usually reduced during turns to
maintain a safe altitude and was subsequently paid-out during the approach to the next line. USBL
performance while towing TACOS was measured in the same maneuvering area but did not include
turns because of reduced steerage at minimal headway. In general, at least 5 min. of data were
collected for each test using Sonardyne Ranger software (Table 1). Shaft RPM and propeller pitch
corresponding to each set of test conditions were recorded by the vessel operators whenever
changes were made.
Early completion of the original test plan allowed supplemental testing with the Klein 5410 towfish.
In particular, the omni-directional transponder was replaced with a directional unit (Table 2) and
USBL performance was measured along an extended straightaway at speeds ranging from 0 (with
towfish hanging in the water column) to 10 kts SOG.
Three methods were used to evaluate USBL signal quality and overall system performance. The first
method applied quality flags stored in the Ranger software to determine the percentage of
transmitted signals that resulted in good navigational fixes. In this case, a code 3 indicated an
acceptable response whereas codes 0 (poor quality overall), 1 (bearing rejected) and 2 (range
rejected) were deemed unacceptable. The second method used post-processed data to determine
the percentage of the total trackline length for which there was usable data. For this analysis,
navigation data were extracted from QINSy and smoothed using a general time domain filter (i.e.
filter 1d in Generic Mapping Tools open-source software3 ). Smoothed navigation data for each of
the towed systems were imported into ArcGIS software where the track lines for each test speed
were then manually split to assemble data for the three layback-angle scenarios. Finally, the plotted

3 See http://gmt.soest.hawaii.edu/
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Figure 5. Smoothed (black) and raw (red) USBL data for an 8 knot tow with the Klein 7180
towed OTS of the vessel (directional beacon). The erratic responses throughout the track are
not usable for side scan image processing.

fixes were examined to subjectively determine the amount of usable data. For example, Figure 5
shows smoothed and raw USBL output from a trackline segment where the majority of fixes were of
poor quality and unusable even after smoothing. Finally, survey log files in Ranger were examined
to assess the effects of propeller pitch and engine RPM on signal quality.
Results
Scientific equipment was installed in Seattle on 27-29 May prior to FA’s departure for the working
grounds. USBL testing occurred 29-30 June and FA returned to Seattle on the evening of 1 July.
The cruise plan was fully executed and some additional testing was also accomplished.